1. Technical Field of the Invention
The present invention relates to a guide apparatus for guiding an advancing continuous fiber bundle, a winding machine for winding the fiber bundle on a bobbin, a method for making a bobbin of a continuous fiber bundle, and the bobbin itself. Specifically, the present invention relates to a winding machine for winding a tape-like fiber bundle having a widened flat cross section on a bobbin and to a bobbin of a continuous bundle of carbon fibers. Further, the present invention relates to a winding machine which is equipped with the guide apparatus and by which a tape-like fiber bundle as a reinforcement can stably be wound on a bobbin in a state wherein the widened flat cross section is maintained.
2. Description of Related Art
As a reinforcement for fiber reinforced composite materials, carbon fibers, glass fibers, aramid (aromatic polyamide) fibers have been used. Among them, carbon fibers have been employed as reinforcement in the uses for aircrafts, sporting-goods such as golf shafts and fishing rods, and supplies in general industries, since the carbon fibers are excellent in specific strength, specific modulus, thermal resistance, and resistance to chemicals. In order to obtain carbon fibers having a high strength and a high modulus, a fiber bundle of carbon fiber precursors which is small in fiber breakage and fluff occurrence, and excellent in qualities is required. Heretofore, as the fiber bundle of precursors, that comprising 3,000 to 24,000 filaments has mainly been employed.
In recent years, carbon fibers came to widely be used up to general industrial uses such as construction, civil engineering, automobiles, energy, and compounds, and thus, so called large tows comprising more than 24,000 filaments having a high strength and a high modulus, and excellent in productivity have strongly been demanded. Carbon fibers are infrequently used only by themselves from the view points of their shapes and other characteristics. In many cases, carbon fibers are impregnated with a resin such as an epoxy resin after a plurality of fiber bundles were arranged in parallel to each other to prepare impregnated fiber bundles (this is generally called as a prepreg), wound into a cylindrical shape or put on a molded product to be covered, and then heated to cure the resin thereby obtain a fiber reinforced plastic molded product as final product.
Since the carbon fibers are light in weight and have a high strength compared with other reinforcing fiber materials, research and investigation have been conducted for further reducing the weight even of a prepreg prepared by impregnating carbon fibers with an epoxy resin to further taking advantage of such characteristics of carbon fibers.
In order to reduce the weight per unit area of a carbon fiber prepreg, it is necessary to widen the carbon fiber bundles to thin, and thus various plans have been elaborated by carbon fiber manufacturers now producing prepregs.
However, if the width of the fiber bundle as a reinforcement, such as carbon fiber bundle supplied at a step for preparing a prepreg was increased in advance up to a certain width, that is, if the fiber bundle as a reinforcement wound on a bobbin was in a shape of widened tape-like fiber bundles, it is possible to omit the work for increasing the width of the fiber bundles at a step of preparing a prepreg. Accordingly, a case wherein a widened tape-like fiber bundle as a reinforcement wound on a bobbin is used for preparing a light stuff prepreg has recently been increased.
Further, in recent years, the application of a bundle comprising a large number of carbon fiber filaments to various molding methods such as drum winding, filament winding, and pultrusion molding has been attempted for preparing a prepreg. Even in these methods for preparing a prepreg, the fiber bundle is preferably in a shape of a widened tape and more desirably in a shape of a fiber bundle which is small in twisting and variation of width.
Such a tape-like bundle of carbon fibers can be produced by impregnating a bundle of carbon fibers with a sizing agent containing an epoxy resin as main component at a last step for preparing carbon fibers, squeezing the impregnated fiber bundle with nip rolls or contacting the impregnated fiber bundle with a dry heated roll to increase its width, and then drying the widened bundle. The tape-like bundle of carbon fibers thus prepared has, as a final product, a shape of a roll wound on a bobbin.
In winding apparatuses, a fiber bundle is traversed in the direction parallel to the axis of a bobbin so that the fiber bundle is uniformly wound in the lengthwise direction of the bobbin. In such existing winding apparatuses, however, consideration is not given to the maintenance of the shape of a tape-like fiber bundle. Accordingly, in a case wherein a widened fiber bundle is wound on a bobbin by employing a winding apparatus designed for general fibers, when a general purpose guide specified by a manufacturer for general fibers was used, the fiber bundle is pressed in the crosswise direction to converge or twisted in the direction of the axis of a bobbin at the time when the fiber bundle is traversed. As a result, the widened tape-like fiber bundle is wound on a bobbin in a state wherein the shape of widened tape-like the fiber bundle was lost, and thus it becomes impossible to apply the winding apparatus to such a purpose preparing a light stuff prepreg as described above.
Then, a proposal has been advanced for winding a widened tape-like fiber bundle on a bobbin by using an existing winding apparatus while maintaining its flat shape. Heretofore, a method in which a guide apparatus is installed as traverse guide in an existing winding apparatus as described, for example, in Laid-open Japanese Patent Publication No. Hei 4-119123 and Laid-open Japanese Patent Publication No. Hei 10-330038 has been proposed.
The guide apparatus described in the Laid-open Japanese Patent Publication No. Hei 4-119123 has a fixed stand for a plate-like yam guide which stand is stood up at a right angle with a traverse arm disposed in parallel to the axis of a bobbin and slid along the traverse arm, and guide rolls for guiding a fiber bundle are disposed above and below the fixed stand yarn guide. The lower guide roll is composed of a single roll disposed in parallel to the axis of a take-up bobbin, and the guide roll disposed above the fixed stand for the yam guide is composed of a pair of parallel guide rolls crossing at right angle with the axial line of the take-up bobbin. While a widened fiber bundle is twisted 90° toward the direction of the axis line of the bobbin between the upper and lower guide rolls, the tape-like fiber bundle can be wound on the bobbin in a state wherein its widened shape is still maintained by passing the fiber bundle through the upper and lower guide rolls.
On the other hand, the guide apparatus described in the Laid-open Japanese Patent Publication No. Hei 10-330038 mentioned above has an upper and a lower cone guides, axial lines of which cross at right angle with each other, disposed above a plate member stood up at right angle with a traverse arm and reciprocatively moved along a traverse arm, and has additionally a pair of upper and lower parallel guides having axis lines almost parallel to that of a take-up bobbin, below the plate member. The fiber bundle is twisted 90° toward the direction of the axis line of a bobbin by means of the plurality of the conical guides disposed above the plate member, advanced through the pair of the guide rolls disposed below the plate member while passing around the pair of the rolls by turn in a state wherein the widened shape is maintained, and then wound on the bobbin.
However, in the guide apparatus described in the Laid-open Japanese Patent Publication No. Hei 10-330038 mentioned above, any consideration is not given to the width of a fiber bundle having a large fineness. In this patent publication No. Hei 10-330038, the apex angle of the cone guides is proposed to be 45° to 120° and preferably 60° to 90°. However, in this range of the apex angle, there is a fear that a sufficient “length” of a roll surface with which a crosswise portion (a line in the crosswise direction) of a fiber bundle contacts can not be secured when a fiber bundle having a large fineness is wound in a case where accommodation of all traverse mechanisms in a space limited from the arrangement of bobbins in a winding apparatus is intended. In other words, when a sufficient length of the oblique line of a conical guide against the width of a fiber bundle having a large fineness was intended to secure in a case wherein the apex angle of conical guide described above was adopted, the diameter itself of the bottom face of the conical guide becomes large, and thus, there is a fear that all of the traverse mechanisms can not be accommodated in the space of a winding apparatus in which a large number of bobbins are already disposed.
Besides, when the guide apparatus described in the Laid-open Japanese Patent Publication No. Hei 4-119123 mentioned above was adopted, the maintenance of the shape of a fiber bundle at the time of reversal in a traverse and winding of a fiber bundle is excellent compared with the case wherein the guide apparatus described in the Laid-open Japanese Patent Publication No. Hei 10-330038 mentioned above is used. However, since the distance between the guide rolls respectively disposed above and below the fixing stand in the guide apparatus is restricted by design specifications and the distance is short, a large torsional force acts on a fiber bundle at the step of twisting the fiber bundle 90° toward the direction of the axis line of a bobbin between the upper guide roll and the lower guide roll, when the number of filaments in one fiber bundle is increased and thus the width of the fiber bundle was also increased. Accordingly, the shape of the widened fiber bundle comes to be lost.
The present invention was produced for the purpose of solving the conventional problems described above, and an object of the present invention is to provide a guide apparatus with which a fiber bundle, as reinforcement for fiber reinforced composite materials, having a width increased into a tape-like fiber bundle can stably be guided in an untwisted condition, and to provide a winding machine with which a widened fiber bundle can stably be wound on a bobbin while maintaining the untwisted condition, sometimes under a condition wherein the width of the fiber bundle is further increased than that of a fiber bundle at the time of being supplied, by merely installing the guide apparatus to an existing winding machine. Another object of the present invention is to provide a method for making a bobbin of a fiber bundle and a bobbin of a bundle of carbon fibers.